Tractors have conventionally been known as a typical work vehicle (see Patent Literature 1). The tractors can travel with an operator operating an accelerator pedal. The tractors can also travel with the operator operating a shift lever and the like. Thus, the tractors travel under an operation suitable for each situation.
When the accelerator pedal and the shift lever or the like are simultaneously operated in the tractor, a traveling state largely changes. Thus, some tractors that have been proposed feature traveling based on an operation on the accelerator pedal (hereinafter, referred to as “accelerator interlocked traveling”) that is selected to be allowed or not. Unfortunately, such a selecting operation may be difficult to understand by an operator and thus might be difficult.
When the tractor that has been stopped starts traveling, what is known as shift shock occurs. The shift shock also occurs when the traveling speed changes due to the driving force generated excessively sensitively in response to an operation of the operator.
Tractors include a continuously variable transmission. Starting and traveling speed can be changed by changing an operation state of the continuously variable transmission. All things considered, there has been a demand for a technique of achieving a drive feeling suitable for the operator with the response speed of the continuously variable transmission being adjustable to prevent the shift shock. However, an operation of adjusting the acceleration characteristics might be difficult because the operator cannot clearly recognize the change as a result of the adjustment.
A technique has been disclosed in which speed is shifted based on an HST gear ratio control curve when a braking operation is performed with a brake operation unit (see Patent Literature 2).
In a tractor, speed of which can be shifted with a hydraulic continuously variable transmission, a frictional main clutch is not included, and power is transmitted from an engine to the transmission by using a damper. In this configuration, half clutch cannot be achieved by operating a clutch pedal, and thus the traveling speed cannot be adjusted in detail. It might be easier for an operator who is used to operating a manual transmission of an automobile to adjust the vehicle speed in detail with the half clutch than with a brake pedal.